Method for distinguishing electrochemical sensors

ABSTRACT

A method for distinguishing between types of electrochemical test sensors in a meter is disclosed. The method comprises the acts of providing an electrochemical test sensor comprising an enzyme and a chemical additive, contacting the test sensor to the meter to form an electrical connection, applying a potential having a magnitude sufficient to initiate a redox reaction of the chemical additive, and determining which type of electrochemical test sensor is being used based on whether a predetermined signal has been generated after the potential has been applied. The meter is adapted to determine an analyte concentration in a fluid sample.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. national phase of International ApplicationNo. PCT/US2006/030626, filed Aug. 4, 2006, which claims the benefit ofpriority of U.S. Provisional Application No. 60/705,903, filed on Aug.5, 2005, which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a method for distinguishingelectrochemical test sensors, and, more particularly, to a method fordistinguishing between multiple versions of electrochemical test sensorsthat utilizes a chemical marker, or chemical additive, in the testsensor.

BACKGROUND OF THE INVENTION

The quantitative determination of analytes in body fluids is of greatimportance in the diagnoses and maintenance of certain physiologicalabnormalities. For example, lactate, cholesterol, and bilirubin shouldbe monitored in certain individuals. In particular, it is important thatdiabetic individuals frequently check the glucose level in their bodyfluids to regulate the glucose intake in their diets. The results ofsuch tests can be used to determine what, if any, insulin or othermedication needs to be administered. In one type of blood-glucosetesting system, test sensors are used to test a sample of blood.

A test sensor contains biosensing or reagent material that reacts withblood glucose. The testing end of the test sensor is adapted to beplaced into the fluid being tested, for example, blood that hasaccumulated on a person's finger after the finger has been pricked. Thefluid is drawn into a capillary channel that extends in the test sensorfrom the testing end to the reagent material by capillary action so thata sufficient amount of fluid to be tested is drawn into the test sensor.Alternatively, the person could apply a drop of blood to the test sensorthat incorporates a reactive zone containing biosensing or reagentmaterial capable of reacting with blood glucose. A voltage is applied,causing the fluid to then chemically react with the reagent material inthe test sensor, resulting in an electrical signal indicative of theglucose level in the fluid being tested. This signal is supplied to asensor-dispensing instrument, or meter, via contact areas located nearthe rear or contact end of the test sensor and becomes the measuredoutput.

A problem occurs when the test sensor is modified, such as, for example,modifying the reagent material. Modified test sensors are typicallynewer test sensor versions with improved features, such as improvedperformance or shortened test times. The modified test sensors mayrequire the meter to apply different calibration information and testingsequences when testing a sample. During the time period before themodified test sensor is to be launched, there exists significantinventory of existing test sensors. Thus, it is desirable that differentversions of test sensors may be used interchangeably in a singleinstrument or meter. Accordingly, the meter should be capable ofdistinguishing between the various versions of test sensors so that theproper calibration information and testing sequences are applied, and anaccurate analyte reading is obtained.

Existing methods for differentiating between different test sensorsversions include requiring a user to perform an affirmative act, such aschanging a code chip or pressing a button on the meter, to signal to themeter that the test strip is a newer version requiring the applicationof different calibration information and/or testing sequences. Therequirement that a user perform an affirmative act to signal to themeter which type of test sensor is being used allows for the possibilityof human error that can adversely affect the analysis of the testresults.

It would be desirable to provide a method for distinguishing betweenmultiple versions of an electrochemical test sensor that would minimizeor eliminate the user's involvement.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a method fordistinguishing between types of electrochemical test sensors in a meteris disclosed. The method comprises the acts of providing anelectrochemical test sensor comprising an enzyme and a chemicaladditive, contacting the test sensor to the meter to form an electricalconnection, applying a potential having a magnitude sufficient toinitiate a redox reaction of the chemical additive, and determiningwhich type of electrochemical test sensor is being used based on whethera predetermined signal has been generated after the potential has beenapplied. The meter is adapted to determine an analyte concentration in afluid sample.

According to another embodiment, a method for distinguishing betweentypes of electrochemical test sensors in a meter is disclosed. Themethod comprises the acts of providing an electrochemical test sensor,contacting the test sensor to the meter to form an electricalconnection, applying a potential ranging from an absolute value of about50 mV to an absolute value of about 350 mV to the test sensor, anddetermining which type of electrochemical test sensor is being usedbased on whether a predetermined signal has been generated. The testsensor includes glucose oxidase and a chemical additive. The meter isadapted to determine a glucose concentration in a fluid sample.

According to yet another embodiment, a method for determining theconcentration of an analyte in a fluid sample is disclosed. The methodcomprises the acts of providing an electrochemical test sensor includingan enzyme, contacting the test sensor to the meter to form an electricalconnection, applying a first potential, determining which type ofelectrochemical test sensor is being used based on whether apredetermined signal has been generated, applying a test sequencecorresponding to the type of electrochemical test sensor, and applying asecond potential to initiate a reaction with the analyte so as to assistin determining the analyte concentration of the fluid sample. The meteris adapted to determine an analyte concentration in a fluid sample. Themagnitude of the first potential is insufficient to initiate a reactionwith the analyte.

The above summary of the present invention is not intended to representeach embodiment or every aspect of the present invention. Additionalfeatures and benefits of the present invention are apparent from thedetailed description and figures set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a test sensor according to one embodiment.

FIG. 2 is a perspective view of a sensor-dispensing instrument or meterin the open position showing a sensor pack being inserted according toone embodiment.

FIG. 3 a is a front view of a disposable cartridge with a plurality ofstacked test sensors according to one embodiment.

FIG. 3 b is a front view of a sensor-dispensing instrument according toone embodiment that is adapted to receive the cartridge of FIG. 3 a.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The present invention is directed to a chemical method fordistinguishing between multiple versions of an electrochemical testsensor. Electrochemical test sensors are used to determineconcentrations of at least one analyte in a fluid. Analytes that may bemeasured include glucose, lipid profiles (e.g., cholesterol,triglycerides, LDL, and HDL), microalbumin, hemoglobin A_(1C), fructose,lactate, or bilirubin. It is contemplated that other analyteconcentrations may be determined. The analytes may be in, for example, awhole blood sample, a blood serum sample, a blood plasma sample, otherbody fluids such as ISF (interstitial fluid), urine, and non-bodyfluids. As used within this application, the term “concentration” refersto an analyte concentration, activity (e.g., enzymes and electrolytes),titers (e.g., antibodies), or any other measure of concentration used tomeasure the desired analyte.

The electrochemical test sensors to be used in determining analyteconcentrations are typically provided with a capillary channel thatextends from the front or testing end of the test sensors to biosensingor reagent material disposed in the test sensor. The reagent may bestored within the test sensor in a dried ink form to promote an extendedshelf life of the test sensor. When the testing end of the test sensoris placed into fluid (e.g., blood that is accumulated on a person'sfinger after the finger has been pricked), a portion of the fluid isdrawn into the capillary channel by capillary action. The fluid thenmixes with the reagent material in the test sensor and chemically reactswith the reagent material so that an electrical signal indicative of theanalyte (e.g., glucose) level in the fluid being tested is supplied andsubsequently transmitted to a sensor-dispensing instrument, or meter.

One non-limiting example of an electrochemical test sensor is shown inFIG. 1. FIG. 1 depicts a test sensor 70 that includes a capillarychannel 72, meter contacts 86, and a plurality of electrodes 76 and 80.The plurality of electrodes includes a working (measuring) electrode 80and a reference electrode 76. The electrochemical test sensor may alsocontain at least three electrodes, such as a working electrode, areference electrode, and an auxiliary or “counter” electrode. Thecapillary channel 72 contains reagent, as will be discussed in moredetail below. Examples of electrochemical test sensors, including theiroperation, may be found in, for example, U.S. Pat. No. 6,531,040assigned to Bayer Corporation. It is contemplated that otherelectrochemical test sensors may be employed.

The electrochemical test sensor 70 also contains an optional triggerelectrode 84, as shown in FIG. 1. The trigger electrode 84 is asub-element of the reference electrode 76. When a fluid sample is placedon the test sensor 70, it first contacts the trigger electrode 84. Theworking electrode 80 and the reference electrode 76 are located furtherdownstream in terms of the direction of sample fluid flow, relative tothe trigger electrode 84. The processor tracks the amount of time ittakes for the fluid to travel from the trigger electrode 84 to theworking electrode 80 and the reference electrode 76 by determining theelectrochemical current time course, which is analyzed by the processor.Based on the current time course, the processor may respond bygenerating the analyte concentration, such as the concentration ofglucose present in the blood sample, or by generating an error codeindicating that insufficient blood sample was present in the sensor tomake the determination.

Electrochemical test sensors of the type known as biosensors include abiochemical recognition element as a sensor reagent. The sensor reagentmay influence items such as the amount of fluid sample needed and thelength of time needed to react with the analyte to determine the analyteconcentration. The reagent generally comprises active ingredients andsupport ingredients. One active ingredient generally includes anappropriately selected enzyme to react with the desired analyte oranalytes to be tested. For example, when the analyte being tested isglucose, electrochemical test sensors may utilize the enzyme glucoseoxidase or glucose dehydrogenase to react with the glucose in thesample. Enzymes used in testing cholesterol concentrations may include,for example, cholesterol oxidase and cholesterol esterase. Anotheractive ingredient generally included in an electrochemical test sensoris a mediator to transfer electrons, such as pyrrolo-quinoline, quinone,glucose dehydrogenase, a ferrocene derivative, (e.g., dimethylferrocene)or a ferricyanide derivative (e.g., potassium ferricyanide,7,7,8,8-tetracyanoquinodimethane, tetrathiafulvalene,N-methylphenazinium, or cobalt hexamine). Mediators may also beappropriate for testing other types of analytes, such as cholesterol.Stabilizing agents may also be added to the sensor reagent to promote alonger shelf life. The reagent of a test sensor used to measure glucose,as one example, utilizes potassium ferricyanide as a mediator andglucose oxidase to react with the glucose in the sample.

To obtain improved electrochemical test sensor performance, theinstrument or meter may be capable of identifying that a new test sensoris being used. New test sensors or new versions of existing test sensorsmay have different assay protocols or programs associated with differentproduct lot numbers. A new test sensor version may require that themeter apply different test sequences, test times, algorithms, voltage,calibration information, or the like. Calibration information associatedwith a test sensor is used to compensate for different characteristicsof test sensors, which may vary on a lot-to-lot basis. Calibrationinformation may be read by the processor before the fluid sample to bemeasured is received. Calibration information may be read by theprocessor after the fluid sample to be measured is received, but notafter the concentration of the analyte has been determined. One methodof determining an analyte concentration of a fluid sample useselectrical current readings and at least one equation. In this method,equation constants are identified using the calibration information orcodes corresponding to the signal generated. These constants may beidentified by (a) using an algorithm to calculate the equation constantsor (b) retrieving the equation constants from a lookup table for aparticular predefined calibration code that is read from the generatedsignal. Variations of this process will be apparent to those of ordinarystill in the art from the teachings disclosed herein, including but notlimited to, the drawings.

According to one method of the present invention, a type or version ofan electrochemical test sensor may be determined by a meter itself,requiring minimal user interaction. An electrochemical test sensor isprovided that includes an appropriately selected enzyme to react withthe desired analyte or analytes to be tested. Additionally, theelectrochemical test sensor includes an appropriately selected chemicaladditive. The type of chemical additive depends on the type of analytebeing tested and is appropriately selected if (1) a redox reaction mayoccur without the presence of a sample including the analyte and (2) theamount of potential typically required for the reaction to occur isreduced. The electrochemical test sensor is then contacted to a meter,which is adapted to determine the concentration of the analyte in afluid sample, to form an electrical connection. A reduced firstpotential is then applied to the electrochemical test sensor. The firstpotential has a first magnitude such that reduction and oxidationreactions of the chemical additive are initiated. The magnitude of thefirst potential is lower than the potential required to test the fluidsample. Applying the first potential initiates the redox reaction,which, in turn, generates a signal. This signal is observed by themeter, and the meter then determines which electrochemical test sensortype or version is being used based on the amount of current generated.The meter may then apply the appropriate test sequence to determine theconcentration of the analyte in the fluid sample.

In one method, the meter generally applies a potential, which is lowerthan that typically required to test the analyte, when it is firstactivated to determine which type of test sensor is in place and whichtest sequence will need to be applied. The activation step can beinitiated by a number of means including a user-operated switch, testsensor insertion, or test sensor presentation from a sensor magazine orcartridge. The meter may then apply this potential every severalmilliseconds until a current is generated. If an older test sensor isused, which does not incorporate a suitable chemical additive, noreaction will occur because the applied potential is too low. Thus, nocurrent is generated. The meter then determines that an older testsensor is being used, and the corresponding standard test sequence andcalibration information are applied. On the other hand, if a new testsensor or test sensor version incorporating a suitable chemical additiveis used, the redox reactions occur, and a current is generated and sentto the processor. The processor determines which new test sensor versionis being used based on the amount of current generated during the redoxreactions. As a result, the processor applies the predefined testsequence corresponding to that test sensor version. Thus, the need for auser to manually change a code chip or press a button corresponding tothe test sensor to indicate to the meter which test sensor is being usedis eliminated.

For example, a first test sensor may be an existing, older version testsensor that includes a first reagent in which an analyte concentrationis determined in a longer time period (e.g., 30 seconds). A user maychoose to use a modified, newer test sensor having a second reagent thatincludes a suitable chemical additive, in which the analyteconcentration is determined in a shorter time period (e.g., 5 to 10seconds). In this method, the meter applies a potential lower than istypically used to test the analyte concentration. The potential is highenough, however, to cause the redox reactions of the chemical additiveto occur. A current is subsequently generated, which is observed by themeter. The meter then recognizes that the test sensor being usedincorporates the second reagent and determines the glucose concentrationin the shorter time period according to the corresponding test sequence.

In one embodiment of the present invention, an electrochemical testsensor for testing glucose in a fluid sample includes a silver salt offerrocyanide (Ag₄Fe(CN)₆) chemical additive. It is contemplated thatother chemical additives including, but not limited to, silver carbonate(Ag₂CO₃), silver bromate (AgBrO₃), iron (III) phenanthroline, butylatedhydroxytoluene (C₁₅H₂₄O), 1,2-benzoquinone, acetaminophen, and ascorbicacid may be used. By incorporating the silver salt of ferrocyanide, thereduction and oxidation reactions shown in Equations 1 and 2 occur evenwithout the addition of glucose and require only a fraction of thepotential applied to test the sample. The reduction reaction, shown inEquation 1, of silver ferrocyanide to silver and ferrocyanide occurs atthe counter electrode, serving as a cathode. The oxidation reaction,shown in Equation 2, occurs at the anode, or working electrode.Ag₄Fe(CN)₆+4e ⁻

4Ag+Fe(CN)₆ ⁴⁻ 0.194 V vs. NHE  (Equation 1)Fe(CN)₆ ⁴⁻

Fe(CN)₆ ³⁻+1e ⁻ −0.460 V vs. NHE  (Equation 2)A potential ranging from an absolute value of about 50 mV to an absolutevalue of about 350 mV (from about −50 mV to about −350 mV) is used forthe reaction to take place. Alternatively, a potential ranging from anabsolute value of about 150 mV to an absolute value of about 250 mV(from about −150 mV to about −250 mV) is used for the reaction to takeplace. The level of applied potential varies depending upon the pairingof reduction and oxidation reactions, the chemical additive selected,and the electrode material. Examples of electrode materials include, butare not limited to, carbon, gold, palladium, and combinations thereof.

It is also contemplated that the polarity may be reversed. For example,some biosensors utilize ferricyanide as a mediator to accept electronsfrom the oxidized form of an enzyme. In such a biosensor, it isadvantageous that the ferricyanide that has been reduced to ferrocyanideby, for example, contamination or instability, be converted back toferricyanide. In such a biosensor with polarity reversed during theinitial potential application, the working electrode initially supportsa reduction reaction while the counter electrode supports an oxidationreaction. If ferrocyanide is present as the additive at the counterelectrode, it is oxidized to ferricyanide during the initial potentialapplication. At the same time, the working electrode reduces silverferrocyanide, silver carbonate, silver bromate, iron phenanthroline,butylated hydroxytoluene, benzoquinone acetaminophen, or ascorbic aciddisposed at the working electrode.

The chemical additive may be incorporated into the test sensor inseveral different ways. Referring back to FIG. 1, according to someembodiments, the chemical additive is incorporated in a separate inkprinted on top of the trigger electrode 84, the working electrode 80, ora combination thereof. The ink in these embodiments may be screenprinted or microdeposited. In other embodiments, the chemical additivemay be a constituent of the trigger electrode ink, the working electrodeink, or the reagent ink. The reagent ink is a separate layer printed ontop of the electrodes. The latter embodiments may be more desirablesince they do not require an additional manufacturing step. The amountof chemical additive may vary but is generally from about 0.1 to about10 nanomoles. It is desirable that the amount of silver salt beminimized so that it sends a signal measurable to the instrument and isconsumed shortly thereafter.

According to one method of determining the glucose level of a fluidsample, the sample is placed on the electrochemical test sensor, whichincludes a potassium ferricyanide mediator and a glucose oxidase enzyme.The glucose in the fluid sample reacts with the glucose oxidase to makegluconic acid and the reduced form of glucose oxidase. The reducedglucose oxidase then reacts with ferricyanide to make ferrocyanide. Theferrocyanide is then oxidized at the working electrode, acting as ananode, by the meter applying, for example, approximately +400 mVpotential relative to the counter electrode. The oxidation reactiongenerates a current that is directly proportional to the concentrationof glucose in the sample. An electrical assembly within the meter thenconverts the amount of current generated into a corresponding glucoseconcentration reading.

A sensor-dispensing instrument, or meter, in one embodiment uses a testsensor adapted to receive a fluid sample to be analyzed. Such a meter 20is shown in FIG. 2. An electrochemical test sensor contacts the meter 20such that an electronic connection is established. The meter 20 alsocontains a processor (not shown) adapted to perform a predefined testsequence for measuring a predefined parameter value. The processor isencoded with calibration information, codes, and/or test sequencesassigned for use in the clinical value computations corresponding toeach test sensor version. A memory is coupled to the processor forstoring predefined parameter data values.

A plurality of electrochemical test sensors is typically stored in adisposable cartridge. For example, the plurality of test sensors may bestored in a test-sensor pack where the test sensors are individuallypackaged in sensor cavities (i.e., a blister-type pack). An example of adisposable cartridge 10 being placed in the meter 20 is depicted in FIG.2. The disposable cartridge 10 is an example of a blister-type pack. Thecartridge 10 includes a plurality of electrochemical test sensors 12that is individually stored in a respective one of a plurality of sensorcavities 14. The cartridge 10 is generally circular in shape with thesensor cavities 14 extending from near the outer peripheral edge towardand spaced apart from the center of the cartridge 10. It iscontemplated, however, that other sensor packs may be of differentshapes than that depicted in FIG. 2. For example, the sensor package maybe a square, a rectangle, another polygonal shape, or a non-polygonalshape, including oval. The disposable cartridge 10 of FIG. 2 is furtherdescribed at U.S. Publication No. 2003/0032190 that published on Feb.13, 2003 and is entitled “Mechanical Mechanism for a Blood GlucoseSensor-Dispensing Instrument.” In this embodiment, each sensor cavity 14accommodates one of the plurality of test sensors 12.

The plurality of test sensors may be stacked in a disposable cartridgesuch as shown in FIG. 3 a. Referring to FIG. 3 a, a disposable cartridge50 includes a housing 52 and a plurality of stacked electrochemical testsensors 54 that is moved in the direction of arrow A via a spring 56.The cartridge 50 also includes a plurality of seals 58 a,b that protectsthe stacked test sensors 54 from humidity. The test sensors 54, one at atime, exit the cartridge 50, via an opening 60. The disposable cartridge50 may be stored in an instrument or meter 70 of FIG. 3 b. It iscontemplated that other cartridges besides cartridges 10, 50 may beused. It is contemplated that the electrochemical test sensors may beused with other instruments or meters than instruments 10 and 70depicted in FIGS. 2, 3 b. The electrochemical test sensors may also beused in other types of sensor packs than sensor package 12. For example,the electrochemical test sensors may be used in sensor packages such asa drum-type sensor package.

Because of the limited shelf life of many test sensors, the cartridges10, 50 of FIGS. 2 and 3 a may vary in the number of electrochemical testsensors that are included so as to address the needs of different users.Typically, the cartridges contain from about 10 to about 100 testsensors and, more specifically, contain from about 25 to about 50 testsensors.

Alternative Process A

A method for distinguishing between types of electrochemical testsensors in a meter, the method comprising the acts of:

-   -   providing an electrochemical test sensor comprising an enzyme        and a chemical additive;    -   contacting the test sensor to the meter to form an electrical        connection, the meter being adapted to determine an analyte        concentration in a fluid sample;    -   applying a potential having a magnitude sufficient to initiate a        redox reaction of the chemical additive; and    -   determining which type of electrochemical test sensor is being        used based on whether a predetermined signal has been generated        after the potential has been applied.

Alternative Process B

The method of Alternative Process A further comprising the act ofmatching the predetermined signal to a corresponding test sequence.

Alternative Process C

The method of Alternative Process A wherein the act of applying thepotential occurs when the meter is activated.

Alternative Process D

The method of Alternative Process A wherein the electrochemical testsensor has a working electrode and a reference electrode.

Alternative Process E

The method of Alternative Process A wherein the electrochemical testsensor has at least three electrodes.

Alternative Process F

The method of Alternative Process A wherein the analyte is cholesterol.

Alternative Process G

The method of Alternative Process A wherein the analyte is glucose.

Alternative Process H

The method of Alternative Process G wherein the chemical additive isselected from the group consisting of silver ferrocyanide (Ag₄Fe(CN)₆),silver carbonate (Ag₂CO₃), silver bromate (AgBrO₃), iron (III)phenanthroline, butylated hydroxytoluene, 1,2-benzoquinone,acetaminophen, and ascorbic acid.

Alternative Process I

The method of Alternative Process G wherein the enzyme is glucoseoxidase.

Alternative Process J

The method of Alternative Process I wherein the absolute values of thepotential ranges from about 50 mV to about 350 mV.

Alternative Process K

The method of Alternative Process I wherein the absolute value of thepotential ranges from about 150 mV to about 250 mV.

Alternative Process L

A method for distinguishing between types of electrochemical testsensors in a meter, the method comprising the acts of:

-   -   providing an electrochemical test sensor, the test sensor        including glucose oxidase and a chemical additive;    -   contacting the test sensor to the meter to form an electrical        connection, the meter being adapted to determine a glucose        concentration in a fluid sample;    -   applying a potential ranging from an absolute value of about 50        mV to an absolute value of about 350 mV to the test sensor; and    -   determining which type of electrochemical test sensor is being        used based on whether a predetermined signal has been generated.

Alternative Process M

The method of Alternative Process L further comprising the act ofmatching the predetermined signal to a corresponding test sequence.

Alternative Process N

The method of Alternative Process L wherein the act of applying thepotential occurs when the meter is activated.

Alternative Process O

The method of Alternative Process L wherein the chemical additive isselected from the group consisting of silver ferrocyanide (Ag₄Fe(CN)₆),silver carbonate (Ag₂CO₃), silver bromate (AgBrO₃), iron (III)phenanthroline, butylated hydroxytoluene, 1,2-benzoquinone,acetaminophen, and ascorbic acid.

Alternative Process P

The method of Alternative Process L wherein the potential ranges from anabsolute value of about 50 mV to an absolute value of about 350 mV.

Alternative Process Q

The method of Alternative Process L wherein the potential ranges from anabsolute value of about 150 mV to an absolute value of about 250 mV.

Alternative Process R

A method for determining the concentration of an analyte in a fluidsample, the method comprising the acts of:

-   -   providing an electrochemical test sensor including an enzyme;    -   contacting the test sensor to the meter to form an electrical        connection, the meter being adapted to determine an analyte        concentration in a fluid sample;    -   applying a first potential;    -   determining which type of electrochemical test sensor is being        used based on whether a predetermined signal has been generated;    -   applying a test sequence corresponding to the type of        electrochemical test sensor; and    -   applying a second potential to initiate a reaction with the        analyte so as to assist in determining the analyte concentration        of the fluid sample,    -   wherein the magnitude of the first potential is insufficient to        initiate a reaction with the analyte.

Alternative Process S

The method of Alternative Process R wherein the act of determining whichtype of electrochemical sensor is being used is based on an absence ofthe predetermined signal.

Alternative Process T

The method of Alternative Process R wherein the analyte is cholesterol.

Alternative Process U

The method of Alternative Process R wherein the analyte is glucose.

Alternative Process V

The method of Alternative Process R wherein act of applying a testsequence includes applying calibration information.

Alternative Process W

The method of Alternative Process R wherein the electrochemical testsensor includes a chemical additive.

Alternative Process X

The method of Alternative Process R wherein the analyte is glucose andthe chemical additive is selected from the group consisting of silverferrocyanide (Ag₄Fe(CN)₆), silver carbonate (Ag₂CO₃), silver bromate(AgBrO₃), iron (III) phenanthroline, butylated hydroxytoluene,1,2-benzoquinone, acetaminophen, and ascorbic acid.

Alternative Process Y

The method of Alternative Process R wherein the first potential rangesfrom an absolute value of about 50 mV to an absolute value of about 350mV.

Alternative Process Z

The method of Alternative Process R wherein the potential ranges from anabsolute value of about 150 mV to an absolute value of about 250 mV.

While the invention is susceptible to various modifications andalternative forms, specific embodiments and methods thereof have beenshown by way of example in the drawings and are described in detailherein. It should be understood, however, that it is not intended tolimit the invention to the particular forms or methods disclosed, but,to the contrary, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of theinvention as defined by the appended claims.

1. A method for distinguishing between types of electrochemical testsensors used in an instrument, the test sensors being configured to beused in determining an analyte concentration in a fluid sample, themethod comprising the acts of: providing an electrochemical test sensorcomprising an enzyme and a chemical marker; contacting the test sensorto the instrument to form an electrical connection, the instrument beingadapted to determine an analyte concentration in the fluid sample;applying a potential having a magnitude sufficient to initiate a redoxreaction of the chemical marker and insufficient to determine theanalyte concentration, the potential being applied by the instrument;and determining which type of electrochemical test sensor is being usedbased on whether a predetermined signal has been generated after thepotential has been applied.
 2. The method of claim 1, further comprisingthe act of matching the predetermined signal to a corresponding testsequence.
 3. The method of claim 1, wherein the act of applying thepotential occurs when the instrument is activated.
 4. The method ofclaim 1, wherein the electrochemical test sensor has a workingelectrode.
 5. The method of claim 1, wherein the electrochemical testsensor has at least three electrodes.
 6. The method of claim 1, whereinthe analyte is cholesterol.
 7. The method of claim 1, wherein theanalyte is glucose.
 8. The method of claim 7, wherein the chemicalmarker is selected from the group consisting of silver ferrocyanide(Ag₄Fe(CN)₆), silver carbonate (Ag₂CO₃), silver bromate (AgBrO₃), iron(III) phenanthroline, butylated hydroxytoluene, 1,2-benzoquinone,acetaminophen, and ascorbic acid.
 9. The method of claim 7, wherein theenzyme is glucose oxidase.
 10. The method of claim 9, wherein theabsolute value of the potential ranges from about 50 mV to about 350 mV.11. The method of claim 9, wherein the absolute value of the potentialranges from about 150 mV to about 250 mV.
 12. A method fordistinguishing between types of electrochemical test sensors used in ameter, the test sensors being configured to be used in determining aglucose concentration in a fluid sample, the method comprising the actsof: providing an electrochemical test sensor, the test sensor includingglucose oxidase and a chemical marker; contacting the test sensor to themeter to form an electrical connection, the meter being adapted todetermine the glucose concentration in the fluid sample; applying apotential ranging from an absolute value of about 50 mV to an absolutevalue of about 350 mV to the test sensor, the potential being applied bythe meter; and determining which type of electrochemical test sensor isbeing used based on whether a predetermined signal due tooxidation/reduction of the chemical marker has been generated after thepotential has been applied.
 13. The method of claim 12, furthercomprising the act of matching the predetermined signal to acorresponding test sequence.
 14. The method of claim 12, wherein the actof applying the potential occurs when the meter is activated.
 15. Themethod of claim 12, wherein the chemical marker is selected from thegroup consisting of silver ferrocyanide (Ag₄Fe(CN)₆), silver carbonate(Ag₂CO₃), silver bromate (AgBrO₃), iron (III) phenanthroline, butylatedhydroxytoluene, 1,2-benzoquinone, acetaminophen, and ascorbic acid. 16.The method of claim 12, wherein the potential ranges from an absolutevalue of about 50 mV to an absolute value of about 350 mV.
 17. Themethod of claim 12, wherein the potential ranges from an absolute valueof about 150 mV to an absolute value of about 250 mV.
 18. A method fordetermining the concentration of an analyte in a fluid sample, themethod comprising the acts of: providing an electrochemical test sensorincluding an enzyme, the electrochemical test sensor including achemical marker; contacting the test sensor to an instrument to form anelectrical connection, the instrument being adapted to determine ananalyte concentration in a fluid sample; applying a first potential, thepotential being applied by the instrument; determining which type ofelectrochemical test sensor is being used based on whether apredetermined signal due to oxidation/reduction of the chemical markerhas been generated; applying a test sequence corresponding to the typeof electrochemical test sensor; and applying a second potential toassist in determining the analyte concentration of the fluid sample, thesecond potential being applied by the instrument, wherein the magnitudeof the first potential is insufficient to determine the analyteconcentration.
 19. The method of claim 18, wherein the act ofdetermining which type of electrochemical sensor is being used is basedon an absence of the predetermined signal.
 20. The method of claim 18,wherein the analyte is cholesterol.
 21. The method of claim 18, whereinthe analyte is glucose.
 22. The method of claim 18, wherein act ofapplying a test sequence includes applying calibration information. 23.The method of claim 18, wherein the analyte is glucose and the chemicalmarker is selected from the group consisting of silver ferrocyanide(Ag₄Fe(CN)₆), silver carbonate (Ag₂CO₃), silver bromate (AgBrO₃), iron(III) phenanthroline, butylated hydroxytoluene, 1,2-benzoquinone,acetaminophen, and ascorbic acid.
 24. The method of claim 18, whereinthe first potential ranges from an absolute value of about 50 mV to anabsolute value of about 350 mV.